– Why do doctors care so much about your BMI when it’s has been proven to be such a flawed metric for ones actual health?
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It’s a way to say “you are damn fat lose some weight” without offending people “you have a high BMI and think we need to do something about that perhaps…”
it’s a flawed metric but that’s why it works.
BMI is a flawed metric for people who are in exceptionally good shape. Body builders and the like are going to have skewed BMIs due to most of their weight being muscle mass.
The average person visiting the doctor is **not** a body builder (citation needed). For them, BMI is a decent _enough_ metric to show whether or not a person is overweight.
People zone-out when doctors start talking about complicated medical things. If its tough to understand, people just ignore it. The BMI is easy to understand, despite its general flaws. So, its better to give someone a general idea of something and have them listen/understand, then give them a complicated and precise explanation that goes way over their head.
Two main reasons –
1) A big part is being able to communicate to your patient and have them understand you. If a doctor took a complicated measurement and tried to tell you that your SJ2099109,.8 test shows 3 teraflaps over a jambo, and therefor you should diet, what the hell does that mean? BMI is at least well understood by everyone in terms *what it means* so it’s an easy way to communicate a medical opinion to a patient.
2) It’s quick, cheap to measure, requires no special equipment, and provides instant results. It’s also easily duplicated, you don’t really have to worry that the “test” was an error or just an “off day” in your measurements. It’s very consistent compared to something as easy as blood pressure or pulse which can change minute by minute or from technician to technician.
BMI is just a formula of weight divided by height, times a constant. Your body weight is equal to the weight of your guts, plus the weight of your bones, plus the weight of your muscles, plus the weight of your fat. For people of similar heights, their guts and bones probably weigh around the same amount, so the difference comes down to muscle and fat.
If you’re an athlete, you have a bunch of muscle, which is dense (it weighs a lot), so your body weight will be higher than someone who doesn’t have muscle or fat. So their BMI will be very high, even though they are extremely healthy. However, 95% of adults are not athletes. If you have two people who are the same height and are about equally active, the one who weighs more is likely going to have more fat on them, and will be less healthy.
So BMI is a quick and convenient way to sort “average” people into buckets that should correlate with their general health. Actually measuring body fat % directly is a difficult and imprecise science, and it doesn’t really matter for almost the entire population.
Doctors, like any other profession, can vary in quality.
Really good doctors will look at all of your body’s data. They understand BMI is only useful in certain situations and will discuss it in those situations. For example, body builders don’t follow the model BMI tries to build and tend to show up as “obese”. Likewise, some people with disorders will likely never have a “healthy” BMI without making unhealthy changes.
Really bad doctors don’t put in that much effort. They take the vitals they have to, poke around, and tell you something that may not be the best advice. Sometimes they miss important signs of underlying conditions and, if you don’t find a better doctor, you may not catch that condition in time.
For example, I read a story about a woman who knew she had some troubling symptoms, but no matter how many times she went to her doctor he told her she needed to lose 40 pounds. There weren’t other doctors in her area and specialists wouldn’t see her without a referral. Her doctor refused to refer her because he was so sure her weight was the problem.
So she lost 40 pounds. He smiled and said, “I bet you feel better now, right?” She didn’t. So then he did some tests, and discovered she had stage 2 ovarian cancer. That would’ve been found if he’d done the tests months earlier.
Bad doctors get away with this because it doesn’t count as malpractice: they can’t be held responsible for not reporting conditions they haven’t seen, and it’s hard to prove there was evidence they should’ve done more extensive tests. There also aren’t really enough doctors. In my area, almost every practice has a 3-6 week lead time for appointments and most aren’t taking new patients. The last time I had to find a new specialist I had to make 9 calls before I found one that could work me in 2 months later. That means a lot of people have to stick with a “not the best” doctor because it’s very hard to find a new one. For capitalism’s “bad service means you go out of business” to take place, people have to have an easy way to choose better service.
So it’s not that doctors in general care so much about BMI. Good ones see it as a tool with a limited use. Bad ones are just taking advantage of their patients’ limited amount of recourse. They’re backed up by society, in general, having little empathy or sympathy for people who are overweight. We like to make fun of overweight people. We consider them lazy and assume if they’d make “better choices” things would get better. So a lot of doctors get a free pass to use weight to write off their patients’ concerns.
Mine did it too. Guess what? I’ve lost 43 pounds over the last year and almost none of my symptoms have changed. I do feel better, I just still have the same problems 3 different doctors have told me don’t exist. If you dig around and read accounts of people who have rare disorders, it’s not uncommon for some people to spend years visiting dozens of doctors before one decides, “Let’s just start testing for everything until we find something.” For some reason, most doctors give up after the obvious tests don’t turn anything up. “You’re overweight” is a good way to justify that.
> it’s has been proven to be such a flawed metric for ones actual health?
It has not been proven to be a flawed metric at all. That’s just BS from the “body positive” movement which thinks that telling people it is OK to be morbidly obese and put yourself at much greater risk of heart disease, diabetes, hypertension, cancer, stroke, and death to be “positive”
Are there exceptions like body builders or whatever who don’t fit the mold for BMI? Sure, but the people crying about BMI aren’t bodybuilders. They are morbidly obese people who think they can redefine words to make them feel better about putting their lives at risk due to their weight.
The people for whom BMI is inaccurate (bodybuilders, extremely tall people) know who they are and their doctors know who they are. For everyone else, it’s a great first pass indicator on whether we need to lose, gain, or maintain weight and how urgently we need to do it.
Activist types insisting that these edge cases make it useless are attempting to muddy the waters around BMI to make it seem like we don’t have a very clear picture of what constitutes excess weight and how bad it is for our health. They do this because they believe combatting social stigma is a more urgent concern than the effects of weight itself.
I actually asked this to my doctor last time I went for a checkup. It turns out that it *is* a good metric, as long you have regular body proportions (i.e. you’re not properly muscular or freakishly broad)
So from a scientific point of view it’s technically flawed because it can’t be applied to a number of demographics, but from a practical perspective the doctor can just view the patient and determine if they are regular enough to be measured through BMI.
One thing I would like to point out which a lot of other answers haven’t touched on is that your BMI is a great indicator of your health at a certain time. Their is no doubt medically that your average person, who does no exercise having a high BMI is more likely to suffer from medical complications. People who are athletes competing in athletic sports tend to be on the higher end with BMI but even then theirs a limit. By analysing fitness patterns you can easily use these numbers to determine how healthy someone’s body is operating.
Doctors know about these flaws, so they can compensate. If you are having actual medical issues they’ll actually put you on a set of scales that can determine your fat amounts.
I am a large majority of muscle, I weigh just above 16 stone. My zero percent body fat will be around 14-15 stone if I had nothing on me left. It’s a pretty terrible indicator for me but it tells me if I’m going up or down – especially if my height grows or changes. My BMI though is about 28, which is not terrible in any sense.
Bodybuilders are about the only major exception to this rule, but bodybuilders also tend to be useless when it comes to cardio intensive activities such as running long distances.
Beyond 35 in BMI, your having medical problems really regardless of your exercise amount. Theirs also a lot of people who claim to do tons of exercise and BMI is a real reality breaker.
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